The present invention concerns a variable exhaust duct for an aircraft turbo-fan type turbojet-engine including a cowling assembly with a door type thrust reverser.
In turbofan engines, the so-called cold flow is ejected from the rear of the engine fan into an exhaust duct or nozzle which comprises an inner wall which actually is the outer surface of an inner cowling surrounding the engine proper and extending downstream of the fan, and of an outer wall, the upstream portion of which is continuous with the cowling which encloses the fan. The inner surface of the outer wall may channel both the bypass flow and the so-called hot, primary flow ejected from the engine proper, either as mixed or confluent flows, or only the bypass flow in the case of so-called separate-flow propulsion systems.
A wall also may fair the exterior surface of the cowling which encloses the fan and the exterior surface of the outer wall of the above described duct. This fairing is especially desirable for powerplants attached under the wings of an aircraft or mounted at the rear of the fuselage. Herein the combination of the outer duct wall and exterior fan cowling will be called the "external cowling".
The present invention relates to a so-called door type thrust-reverser of the type disclosed in French patent Nos. 1482538 and 2030034 and U.S. Pat. No. 3,605,411, wherein reverser doors, when in the closed position, are integrated into the engine cowling wall when in the forward thrust mode, but which may be pivoted to reversed thrust positions. The pivoting motion may be about lateral pivots and the doors may be driven by displacement control means such as, for example, linear actuators, so that the doors, when pivoted into the reversed thrust position, deflect at least part of the turbofan exhaust flow through a space constituting an outlet opening or reversal well with a forward component to attain thrust reversal.
Examples of this type of thrust reverser for turbofan type engines wherein the thrust reversers are provided with pivoting doors are disclosed illustratively in French patent documents 2618853; 2618852; 2621082; 2627807; 2634251; 2638207 and 2651021 owned in common with this application.
The thrust-reversal performance of such known devices is generally satisfactory.
However, there remains a problem in matching the engine output to the various flight phases encountered, particularly aircraft takeoff and landing, during which times the cross-sections of the bypass exhaust duct which were suitable for cruise flight may no longer be acceptable. By way of illustration, French patent 2622929 solves this problem using a cascade thrust-reverser. However, the problem remains for thrust reversers which use a plurality of deflector doors.